1. Field of the Invention
The invention is in the field of irrigation control systems for agricultural purposes, and particularly relates to drip irrigation emitters, which provide irrigation of plants and trees at relatively slow rates.
2. Description of the Prior Art
The concept of drip irrigation was developed several years ago as a technique for irrigating plants and trees with a minimum of water. According to this concept, fluid supply lines are fitted with devices, known as emitters, which are placed in close proximity to plant root areas. Drip emitters, as distinguished from water sprinklers, spinners or spitters, emit a very small volume of water per unit time. This slow flow rate of fluid discharge allows the soil to fully absorb the water where it is moved by capillary action. As is known to those skilled in the art, excessive flow rate leads to water waste through run off and evaporation. Water run off has the additional disadvantage that excess watering of down slope plants and trees occurs where plants and trees grow on hilly terrain.
For an emitter to be truly effective, several design criteria must be met. Emitters must permit water application at predetermined constant flow rates so as to limit the flow of water across the soil surface, yet provide sufficient mositure to meet the demands of the plants and trees.
They should also be self-cleaning, that is, they should include an internal system which automatically removes water carried minerals and organic matter deposited on emitter parts. Since the emitter outlets through which water flows are small, they often become clogged by foreign matter carried by the water. Any restriction in water flow through the emitter can upset the uniformity of water distribution causing plant damage before the restriction can be detected. The self-cleaning feature allows for the automatic removal of deposited foreign substances.
The emitter should allow the predetermined output flow rate to remain relatively constant, independent of variation in input water pressure. It is also highly advantageous if the predetermined flow rate could be easily and quickly varied over a wide range. Along with the above listed criteria, emitters should provide a positive shut-off against the back flow of water from the main supply line after the main supply is shut off. This feature is particularly important in steep slope areas where the water line is drained through lower emitters after water shut-off, resulting in a waste of water and/or nutrients dissolved in the water used for the fertilization of plants during the irrigation process.
Although various emitters are known, such as those shown in U.S. Pat. Nos. 3,685,735, 3,719,327 and 3,810,582, none have been designed to successfully meet all of the above design criteria.